Immunity finding to help stem spread of viruses

SCIENTISTS have discovered how mosquitoes develop viral immunity - a significant finding with the potential to halt the spread of crippling mosquito-borne viruses, such as dengue and West Nile.

Researchers from CSIRO's Australian Animal Health Laboratory in Geelong showed that a protein called vago is released by infected mosquito cells. It warns other cells to fight the invading virus, effectively giving the insect's immune system a heads up.

''It's front-line defence,'' said virologist Peter Walker, who worked on the research over 18 months with colleague Prasad Paradkar.

Before the discovery, little credit was given to the mosquito, which was not thought to have much of a natural defence. Instead it was considered that a virus infecting mosquitoes went easily onto its host because it was critical to transmission.

Instead researchers found mosquitoes are able to detect infection by a virus, then they secrete vago, which binds to the surface of cells and turns on the anti-viral response.

''This is a fundamental discovery as it changes the way we think about controlling these diseases,'' Professor Walker said. ''It allows us to shift our thinking and attack the diseases in a different way.''

Mosquitoes spread viruses such as dengue fever, Ross River virus, Murray River encephalitis and West Nile virus - threatening the health of people, livestock and wildlife.

Dengue infects about 75 million people around the world, killing about 22,000 a year.

Professor Walker said another virus, called chikungunya, has been spreading rapidly out of Africa and through Asia with some concern that it could enter northern Australia.

Published in the current issue of the Proceedings of the National Academy of Sciences, the discovery will be used to harness the mosquitoes' natural defence system to make them more resistant to the viruses.

''It may be that we can come up with really novel ways of treating these very important diseases,'' Professor Walker said. ''Our work is not so much about how you might treat humans but how you might attack the mosquito. If you can make the mosquito super-resistant to viruses so that when they became infected, they were not as effective in transmitting the disease.''

Vago has been identified in fruit flies and other invertebrates, and exists in the body at all times at a low level. The level rises when infection strikes.

The findings could also prove useful to the aquaculture industries in Australia and overseas.